Probiotics, healthy bacteria, and healthy micro-organisms in fermented foods will improve IBS caused by bacteria imbalance as well as candida overgrowth. You should be able to buy probiotics in the refrig section of the health food store. Making kefir, yogurt, kombucha, and fermented vegetables are ways to ensure that you are getting active cultures. This is how Jordan Rubin cured his colitis. We are actually the only culture in history that doesn't have a major food source providing these microbes to our bodies, and I think that has caused bacteria/yeast problems to be incredibly common.